Many commonly used chemicals are produced and sold in pulverulent form, but are then slurried, dispersed, or dissolved in water when used by the consumer. Examples of these materials are pesticides (specifically insecticides, herbicides, nematicides, and fungicides, and the like) which are applied as a water spray, cleaning products (such as laundry detergents, bleaches, and caustic cleansers) which are dissolved in wash water, process chemicals (such as carbon black and activated charcoal) which can be slurried in water, and pigments and dyes which are dissolved or dispersed.
There are several problems associated with the use of these types of products. The first of these problems is exposure of the user and his immediate surroundings to the chemical. Opening a package of finely ground material, measuring an amount of the material, and transferring the measured amount from the package to the equipment where the material is contacted with water can generate airborne dust which contacts the user and contaminates the area. A pesticide dust could be irritating to the eyes and mucous membranes of the nose and throat of the user. A herbicide dust could damage plants in the area where the packages are opened. Dusts of pigments or activated charcoal present severe clean-up problems.
The second problem in using common pulverulent chemicals is accuracy of measurement. Clearly, overcharging of expensive materials is costly. Use of a weak solution of a herbicide will not properly control the undesired plant species. Use of too strong a solution of the same material may damage some desired plants as well as the undesired weeds. It is frequently extremely difficult to accurately measure materials which have become compacted and/or lumpy and to transfer powdery materials in areas exposed to wind.
Finally, after the chemical has been used, the user is faced with the problem of disposing of the package in which the chemical was delivered. It may contain residual amounts of a material which is a pollution problem, potentially hazardous to humans, harmful to plants and animals, or merely unpleasant and unsightly.
Currently available water-soluble films and packages possess one or more of a variety of deficiencies such as the following:
(a) Many films which are characterized as water soluble dissolve slowly or dissolve incompletely in cold water, resulting in the formation of gel-like particles. These particles tend to deposit on vessel walls, piping, pumps, and valves and restrict or prevent flow through screens and nozzles. The melt-extrudable films of this invention are rapidly and completely soluble in water at temperatures as low as 4.degree. C. and do not form gel-like particles of undissolved or partially dissolved polymer.
(b) Many of the compositions utilized in the preparation of such films possess physical properties which are such that large, expensive, highly energy consuming and technologically complex process equipment for film manufacture, e.g., solvent-casting (or doctor knife or bandcasting) is required. A typical solvent-casting process involves dissolving the composition in a suitable solvent (e.g., water), spraying or pouring and spreading the composition on a moving belt, drying the composition, generally, by evaporation of the excess solvent, stripping the dried film from the moving belt and then cutting or shaping into the desired form. The technological complexity of such a process is self-evident. Also that process equipment performing so many steps would be large and expensive is equally clear. However, in consideration of current costs and availability of energy, perhaps even more significant is that a process step involving drying by evaporation of large quantities of water will require the expenditure of enormous amounts of energy.
Preferable to such preparation methods is melt extrusion. Melt-extrusion process equipment compared to the equipment used in water casting, is extremely small, inexpensive, technologically simple, and consumes very little energy.
(c) Many water-soluble films of the prior art possess physical properties which make the film unsuitable for use in packaging quantities of pulverulent materials in the range of one half to ten pounds (e.g. yield strength, tear resistance, toughness, flexibility). Such films are also unsuitable for use in automatic packaging machinery.
(d) The constituents of many of the water-soluble packaging films currently available are numerous, difficult to obtain, and/or expensive.
(e) Examples of prior art teachings include Japanese Pat. No. 28,588/69, U.S. Pat. No. 3,374,195, and its divisional U.S. Pat. No. 3,413,229, and United Kingdom Pat. No. 1,330,745.
The Japanese Patent teaches that a melt-extrudable water-soluble film can be made from a polyvinyl alcohol having viscosity of 18 cps.+-.2 and any of many polyols. Certain draw and melt temperature restrictions are taught. These films include many which are not rapidly water soluble, many which exude upon melt extruding, and many which are not suitable as water-soluble packaging film.
U.S. Pat. No. 3,374,195 teaches an aqueous cast film which is hot or cold water soluble. The film consists of PVA and a combination of two plasticizers, which is a polyethylene glycol of mw 200-600 and hydroxypropyl glycerine. This patent does not teach that the composition is melt extrudable and does teach hydroxypropyl glycerine as a necessary coplasticizer.
The United Kingdom Patent teaches an aqueous cast film which is hot or cold water soluble. The film consists of PVA and a combination of polyvinyl pyrrolidone and an optional plasticizer. This patent does not teach that the composition is melt extrudable and does teach polyvinyl pyrrolidone as a necessary constituent.